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Here is my thread on composite fuse repair

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Here is my thread on composite fuse repair

Old 09-23-2005, 04:01 PM
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Default Here is my thread on composite fuse repair

Hey guys, here is the link to a thread I did on fixing my Comp-Arf. I thought it might be useful to you guys.

http://www.rcuniverse.com/forum/m_3379769/tm.htm
Old 09-25-2005, 02:45 PM
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Default RE: Here is my thread on composite fuse repair

In addition to the previous post try this one.

http://www.rcpro.org/net/ThreadView.aspx?threadid=405

Ed S
Old 09-28-2005, 05:38 PM
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Default RE: Here is my thread on composite fuse repair

Nice job Ed!
Old 10-10-2005, 11:25 PM
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Default RE: Here is my thread on composite fuse repair

Darrin and Ed,
I understand the process of repairing a hole but what about a composite fuselage that has had some crushing damage. It is a patter fuselage that is glass/foam/glass. The glass on both outside and inside of the fuselage has not broken, or at least not to the eye. It looks like the foam in the sandwich got cracked between the glass. The part of the sandwich that is damaged looks like a ripple from the outside "damaged foam is compressed in towards the inside of the fuselage". If you stick your hand in the fuselage and push out slighly on the backside of the damage the ripple disappers make it look like no damage. What would be the best "ie simplest" way of repairing this damage. I do plan on running a light balsa bridge from the tail former to servo tray after the repair to strengthen the fuselage against being compressed. Any pointers would be appreciated. I can get some pictures of the damage if that would help.
Old 10-11-2005, 12:33 AM
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Default RE: Here is my thread on composite fuse repair

Ed and Darrin,

I have been looking at the composite section here on RCU. There are a lot of repair articles on composite ARF fuselage repairs. Looking at those techniques and think about this fuselage I have an Idea.

1: Use .25 in square balsa stick cut in about 1 to 1.5 inch pieces. Glue them to the outside of the fuselage half on the solid part of the fuse and half on the damaged part of the fuselage. This will put help keep the damaged and undamaged parts lined up.

2: I have a Hobbico woodpecker tool. Used to put small holes in balsa before covering. It could be used on the inside to perforate the damaged/undamaged area allowing epoxy to get into the foam area. This could be done without damaging the gel coat on the outside.

3: Prep the area on the inside. Sand and clean with alcohol.

4: Using a brush, apply epoxy to the inside area. Use a credit card and scrap the extra epoxy away. My thinking in doing this would force epoxy into the foam through the perforations. Then put down a layer of 2oz cloth. When that cures, clean and lay on a 45 diagonal another layer of 2oz cloth.

5: Remove balsa sticks and lightly sand area trying not to damage the gel coat.

6: Fill any possible imperfections on the outside, sand, prime, and paint.

Do you think I am on the right track?
Old 10-11-2005, 06:53 AM
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Default RE: Here is my thread on composite fuse repair

You still need to put cloth on both the inside and outside, otherwise your repair will buckle. It works best if you balance your layup, do the same layup on the inside as the outside. This is probably not super critical for our models, but it is good practice and you might as well learn to do it right.
Old 10-11-2005, 07:47 AM
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Default RE: Here is my thread on composite fuse repair

Darrin,
Even though the glas and the glecoat on the outside is not damaged? Wouldnt the epoxy getting into the foam and a layer of glass strengthen it enough so that if I were to put in a bridge or former it could not crush again? Just asking, I just hate the thought of messing the outside gelcoat up. If I really do have to put glass on the outside do I leave the exterior gel coat and glass alone or do I do the same treament out side that I am doing on the inside?
Old 10-12-2005, 03:08 PM
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Default RE: Here is my thread on composite fuse repair


ORIGINAL: Darrinc

You still need to put cloth on both the inside and outside, otherwise your repair will buckle. It works best if you balance your layup, do the same layup on the inside as the outside. This is probably not super critical for our models, but it is good practice and you might as well learn to do it right.

This isn't true in the case of a sandwich repair. The outer skin of the sandwich in this case has been crippled, and is not contributing stiffness to the sandwich. In that situation, the sandwich has an altered load path through the core and into the other skin (presuming that the delam is large enough to allow shear transfer through the core and not simply bypass). In this case, an overlap patch repair on the outside (OML) of the plane that closely replicated the stiffness of the original skin would provide adequate stiffness and would not deform the skin. However, the real key to making this a sucessful repair is ensuring that the delamination doesn't grow between the skin and the core. I think that the injection of epoxy into the void would likely provide adequate filling, but a material that foamed would probably do a better job of filling the damaged core.

I would be very careful adding an additional longeron on the inside. You want to locally reinforce the damaged area, not globally stiffen one side of the aircraft. The right thing to do is to carefully remove the damaged outer skin, remove the damaged core, bond in a new section of core, create a plug that is the same shape and layup as the outer skin and bond that on top of the core, and then bond on a patch doubler over that (of the same layup as the skin). Of course, that would require you to damage the gelcoat, but it would be much more likely to survive.

Matt
Old 06-27-2007, 03:17 PM
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Default RE: Here is my thread on composite fuse repair

Any idea on how to repair this. It is a Sig Cap 231 1/4 scale cowl. someone put too large an engine in it. I would like to repair it and start over on cutting the correct holes. any suggestions would be helpful. It does have some compound curves. looking from side and starting at firewall it is flat then curves up toward nose. Looking from front it has nice rounded corners.
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Old 06-27-2007, 03:42 PM
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Default RE: Here is my thread on composite fuse repair

This is what I would do. Clean out and degrease the inside of the cowl. Cut a piece of 6oz glass cloth about 1/2 bigger all round than the hole following the contours of the cowl. Tack glue the cloth on the inside of the cowl. Try and manipulate the cloth so it follows the cowl contours without exceeding the outer cowl profiles. when tacked in place very carefully brush on a coat of epoxy resin. When cured carefully spread a mix of resin and micro balloons over the cured patch. Now it is just a question of filing, sanding, filling as many times as it takes to reproduce the cowl shape. It may be necessary to add some more reinforcing glass to the inside.

OR buy a new cowl from Sig.

Ed S
Old 06-28-2007, 09:38 AM
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Default RE: Here is my thread on composite fuse repair

Ed Smith,

Thanks for the info. I already contacted sig and they no longer carry this item. I also contact fiberglass specialties and they don't have a cowl either. they do have a few that might work but they are a bit larger. I think I will try to repair it and if the plane survives long enough i might buy a larger cowl.

thanks again,

Josh
Old 06-28-2007, 11:36 AM
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Default RE: Here is my thread on composite fuse repair

How about build a box around the opening, pour in pour-able foam (or carve some blocks to fit), shape the foam to the shape you need, fiberglass the outside, then cut out (or melt out) the foam? For this pourpose, the PVC floral foam (the rigid stuff) you can acquire at a girly hobby store should work just fine.
Old 06-28-2007, 06:05 PM
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Default RE: Here is my thread on composite fuse repair

ORIGINAL: TeamSeacats

How about build a box around the opening, pour in pour-able foam (or carve some blocks to fit), shape the foam to the shape you need, fiberglass the outside, then cut out (or melt out) the foam? For this pourpose, the PVC floral foam (the rigid stuff) you can acquire at a girly hobby store should work just fine.
Yup...This will work well...I have been in a similar situation and I did the "Block" concept..I used PVC floral foam from the girly store..he he...The way to go IMHO...You have a lot of contour/surface area to re-produce...

One note of *My Experience*...
A long time ago I tried that spray expandable foam in a can from Lowes or Home Depot or whereever...It's called "Great Stuff"...I was *Attempting* to use it to re-enforce my Ultimate Bipe's plastic cowl and wheel pants so I could make molds off them...I thought this would be some "Great Stuff" for that application...Ahhhhh NO...At least in my case it wound up ballooning the parts out of shape quite badly...Then it was really hard to get out...I would call it a "pain in the arse"

I attempted to use it "sparingly" and *Assumed" it would expand out the big open hole in the cowling...Ahhhhhh NO

I'm not saying that pour-able foams are not good...I have used them in Composite Tooling applications at my Day Job way back when...But this was stuff that you and I probably don't wanna buy ($$$$$$)...There may be some good pour-able foams available for hobby type work out there??

I just wanted to give you a bit of "Heads Up" about the Great Stuff...

Of course I could have done something wrong...Maybe others would have better luck...That was just *My Experience*

Have Fun!!

Chuck
Old 06-28-2007, 07:12 PM
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Default RE: Here is my thread on composite fuse repair

I second that..."Great" stuff is "Great" for sealing a crack around a window. It is not "Great" for composite work.
Old 07-03-2007, 09:21 AM
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Default RE: Here is my thread on composite fuse repair

I tried the "Great Stuff" on friday. Oh I wish I had gotten to your post before I tried that. You are right it expands and distorts your part and not easy to get out. I tried gasoline to dissolve the foam with no luck. I even used acetone (nada). I eventually got it out. I then just laid a piece of fiberglass inside the cowl and tacked it down around the perimeter with thin CA. This was my first time ever attempting a glassing project. I have read numerous articles about it so therefore under stand how FG gets its strength. I then wet the glass and forced a balloon into the opening and was able to produce a pretty acceptable contour. It is not exactly scale but will be better than it was. The only problem was the balloon stuck too the cowl. I used the heat gun to shrink the balloon off of the epoxy once it cured. The next step was another layer of fg and then microballoons. It finally looks pretty good after some sanding. I still need to fill a few more low spots then the whole prepping and painting. I will post a pick when I get a chance. I am pleased. And like I said I just wanted it to look better than it did, I wasn't expecting to get it perfect.

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